1. Field of the Invention
The present invention relates to an image sensor having a plurality of photoelectric conversion devices each including a plurality of light-receiving elements and a method of driving the same and, more particularly, to an image sensor having a resolution switching function and a method of driving the same, a photoelectric conversion device used in the image sensor, and an image reading apparatus such as an image scanner, facsimile apparatus, or electronic copying machine for reading a two-dimensional image.
2. Related Background Art
Recently, in the field of data processing systems, one-to-one type image sensors each having a plurality of semiconductor photosensor chips have been extensively developed as one-dimensional image readers in place of reduction-type line sensors each using a conventional optical system.
For example, Japanese Patent Application Laid-Open No. 5-227362 has proposed a contact-type image sensor which has a new resolution control terminal and allows the user to select a desired resolution in accordance with a use condition.
FIG. 1 is a circuit diagram of a contact-type image sensor integrated circuit proposed in Japanese Patent Application Laid-Open No. 5-227362. In this arrangement, a control terminal 125 is formed on an image sensor chip. The user inputs a signal of high or low level to this terminal to select a high or low resolution mode. This will be briefly described with reference to FIG. 7. A start pulse SI and a clock pulse CLK are supplied to a shift register group 104. When a shift register 104a is activated in response to the start pulse SI, its output is input to a channel select switch 103a via a NOR gate 121a and an AND gate 120a. The NOR and AND gates 121a and 120a are turned on to extract a signal from a photocell 101a to a signal line 107a. The remaining shift registers 104b to 104f are sequentially activated to output signals from photocells 101b to 101l to the signal line 107a or a signal line 107b. 
When a control signal xe2x80x9cHxe2x80x9d is input to the control signal input terminal 125, analog switches 110a, 110b, 122a, and 122b are switched to obtain an image signal at an image output terminal 111 at a read density of 16 dots/mm. When a control signal xe2x80x9cLxe2x80x9d is input to the control signal input terminal 125, the analog switch 110a is always set in the ON state to obtain an image signal at the image output terminal 111 at a density of 8 dots/mm which is half the density of the photocells 101a to 101l. That is, although all the photocells 101a to 101l on the sensor IC are always operating, some outputs are thinned out by the control signal in externally extracting the output image signal. Therefore, the image signal voltage level is always kept constant, and a conventional arrangement can be used for the subsequent image processing circuit.
To meet high-speed operation, for example, Japanese Patent Application Laid-Open No. 2-210950 has proposed an image sensor chip having a means for delaying a start signal, and a contact-type image sensor using this image sensor chip. A constant current circuit is started before a sensor signal is read to achieve a high-speed read. More specifically, there are provided an image sensor chip used in a multichip photoelectric conversion device obtained by arranging a plurality of image sensor chips having light-receiving elements, and a photoelectric conversion device using this image sensor chip, characterized in that a delay means for delaying a start signal for light signal read operation using the light-receiving elements and a constant current circuit having a signal used for the start signal for the image sensor chip and arranged in an amplifier circuit for amplifying the light signal read signal using the light-receiving elements are turned on before the end of the light signal read operation in accordance with a start signal representing the start of delay of the delay means.
Japanese Patent Application Laid-Open No. 2-210949 discloses a one-chip arrangement used in Japanese Patent Application Laid-Open No. 2-210950. More specifically, this reference has proposed an image sensor chip for driving a shift register using an internal clock "PHgr"1 synchronous with high level of a clock signal and an internal clock "PHgr"2 synchronous with low level of the clock signal, and a contact-type image sensor using this image sensor chip, thereby realizing a high-speed read at a duty ratio of 100%.
FIG. 2 is an equivalent circuit diagram of an image sensor chip assumed from the contents described in Japanese Patent Application Laid-Open Nos. 2-210949 and 2-210950.
Referring to FIG. 2, a plurality of photoelectric conversion devices 1, 1xe2x80x2, and 1xe2x80x3 are mounted on the image sensor chip, and a clock CLK and start pulse SP for driving each photoelectric conversion device are commonly supplied to the photoelectric conversion devices 1, 1xe2x80x2, and 1xe2x80x3. The photoelectric conversion devices 1, 1xe2x80x2, and 1xe2x80x3 respectively comprise N-bit delay means (n-bit preshift registers 2, 2xe2x80x2, and 2xe2x80x3), k-bit shift registers 3, 3xe2x80x2, and 3xe2x80x3, k-bit light-receiving element arrays 4, 4xe2x80x2, and 4xe2x80x3, timing generation circuits 5, 5xe2x80x2, and 5xe2x80x3, and signal output amplifiers 6, 6xe2x80x2, and 6xe2x80x3.
Next-chip start signals 9, 9xe2x80x2, and 9xe2x80x3 output signals N bits ((K-N)th bit) before the end of read by bits of the photoelectric conversion devices as the start signals for the next chips from the bit position N bits before the last register of the shift registers 3, 3xe2x80x2, and 3xe2x80x3.
The timing generation circuits 5, 5xe2x80x2, and 5xe2x80x3 driven by the clock CLK and the start pulse signal SP generate pulses for driving the light-receiving elements 4, 4xe2x80x2, and 4xe2x80x3, and the drive pulses "PHgr"1 (7, 7xe2x80x2, and 7xe2x80x3) and "PHgr"2 (8, 8xe2x80x2, and 8xe2x80x3) for driving the shift registers 3, 3xe2x80x2, and 3xe2x80x3. The start pulse signal SP is commonly supplied to the respective image sensor chips so as to synchronize the start of operations of the respective image sensor chips.
The signal output amplifiers 6, 6xe2x80x2, and 6xe2x80x3 amplify image signals read from the light-receiving element arrays 4, 4xe2x80x2, and 4xe2x80x3 onto a single signal output line via switches which are turned on/off in accordance with shift signals from the shift registers. The amplified signals are converted into signal outputs Vout in accordance with the control signal from the timing generation circuits 5, 5xe2x80x2, and 5xe2x80x3. Constant current circuits are arranged in the signal output amplifiers 6, 6xe2x80x2, and 6xe2x80x3 and receive the voltage simultaneously with the input of the start signal. The constant current circuits allow the amplifiers to perform steady amplification operations when the clock signals each succeeding N bits from the start signal are input.
FIG. 3 is a timing chart of the drive pulses "PHgr"1 (7, 7xe2x80x2, and 7xe2x80x3) and "PHgr"2 (8, 8xe2x80x2, and 8xe2x80x3) for the shift register 3 with reference to the clock CLK.
Note that FIG. 3 shows the timings when the delay means in FIG. 2 has a 4-bit arrangement. The operation of the first one of the shift register 3, 3xe2x80x2, or 3xe2x80x3 starts with a delay of 4 bits from the start pulse signal SP.
As shown in FIG. 3, the drive pulse "PHgr"1 (7, 7xe2x80x2, and 7xe2x80x3) is synchronized with high level of the clock CLK, while the drive pulse "PHgr"2 (8, 8xe2x80x2, and 8xe2x80x3) is synchronized with low level of the clock CLK. The signal output Vout is extracted in synchronism with the drive pulses "PHgr"1, and "PHgr"2. When the first bit of the shift register 3 corresponds to the drive pulse "PHgr"1, the odd- and even-numbered bits of the signal output are synchronized with the drive pulses "PHgr"1 and "PHgr"2, respectively.
Signals A, C, and E are signal outputs from the photoelectric conversion devices 1, 1xe2x80x2, and 1xe2x80x3, respectively. The signal output Vout as the sum of the signals A, B, and C is shown in FIG. 3. The signals each four bits before the last bit in each photoelectric conversion element are output as start signals B and D of the subsequent photoelectric conversion devices.
A large original can be directly read as a multichip contact-type image sensor to eliminate idle times between read operations of the chips and differences between signal output levels.
In the resolution switching scheme of the contact-type image sensor shown in FIG. 1, pixels are skipped in a read to change the resolution. For example, when the clock rate is kept unchanged, the read time with the normal resolution is equal to that with xc2xd the normal resolution. Assume that the light-receiving elements are arranged at an optical resolution of 600 dpi, and 600 dpi and 300 dpi are set in the high and low resolution modes, respectively. when a read rate of 6 msec/line is set at 600 dpi, the read rate at 300 dpi is also 6 msec/line. The read rate is kept unchanged even with a decrease in resolution. The read rate does not change depending on the resolution at the same clock rate, i.e., the read rates of 5 msec/line at 600 dpi and 3 msec/line at 300 dpi cannot be realized at the same clock rate.
Since the signal output lines for odd and even bits are separate, the level difference between the even and odd bits tends to occur.
When the resolution switching technique shown in FIG. 1 is applied to the contact-type image sensor shown in the arrangement shown in FIG. 2, discontinuities are formed between the joint portions of the photoelectric conversion devices in switching the resolution.
In the arrangement shown in FIG. 2, when the number of bits of a preshift register is, e.g., 10, the output of the first bit of the next photoelectric conversion device is output 10 bits after the output of the next-chip start signal in the high resolution mode. In this case, the signal is not discontinuous in the joint portion between the adjacent photoelectric conversion apparatuses. In the low resolution mode, since the signal output ends 5 bits after the next-chip start signal is output, a discontinuous portion of 5 bits is formed in the joint portion between the adjacent photoelectric conversion devices until the output of the first bit of the next photoelectric conversion device appears. It is difficult to obtain continuous image signals at high and low resolutions even if the arrangement in FIG. 2 is used for the arrangement in FIG. 1.
It is an object of the present invention to provide an image sensor which has a plurality of photoelectric conversion devices each including a plurality of light-receiving elements, can attain the read rate corresponding to the resolution and is free from discontinuity at a joint portion between the adjacent photoelectric conversion devices, a photoelectric conversion device suitable for the image sensor, an image sensor driving method, and an image reading apparatus using the image sensor.
In order to achieve the above object, according to an aspect of the present invention, there is provided an image sensor having a plurality of photoelectric conversion devices each including a plurality of light-receiving elements, comprising scanning means for reading a signal from the light-receiving element; delay means for delaying a start signal of the scanning means; resolution switching means for switching a resolution of a signal read from the light-receiving element; start signal output means for outputting a plurality of types of start signals for the scanning means of the next photoelectric conversion device before an end of read operation of the scanning means in accordance with switching of the resolution switching means; and start signal switching means for switching the plurality of start signal output means.
According to another aspect of the present invention, there is provided a method of driving an image sensor including a plurality of photoelectric conversion devices each having a plurality of light-receiving elements, scanning means for reading a signal from the light-receiving element, and resolution switching means for switching a resolution of the signal read from the light-receiving element, comprising a step of outputting a start signal for the scanning means of the next photoelectric conversion device before an end of read operation of the scanning means in accordance with a resolution.
According to still another aspect of the present invention, there is provided an image sensor having a plurality of photoelectric conversion devices each including a plurality of light-receiving elements, comprising resolution switching means for switching a resolution of a signal read from the light-receiving element; scanning means for reading a signal from the light-receiving element in accordance with the resolution switched by the resolution switching means; and start timing control means for controlling a start timing from one of the photoelectric conversion devices to the next photoelectric conversion device in accordance with the resolution.
According to still another aspect of the present invention, there is provided a photoelectric conversion device having a plurality of light-receiving elements, scanning means for reading a signal from the light-receiving element, and resolution switching means for switching a resolution of the signal read from the light-receiving element, wherein a start signal is output as a read timing signal in accordance with a read timing of a predetermined light-receiving element before a last read light-receiving element of the plurality of light-receiving elements, and the read timing is switched in accordance with switching of the resolution.
According to still another aspect of the present invention, there is provided a photoelectric conversion device comprising a light-receiving element array in which a plurality of light-receiving elements are arranged, scanning means driven by a first shift register drive pulse for reading a signal from an odd-numbered light-receiving element of the light-receiving element array and a second shift register drive pulse for reading a signal from an even-numbered light-receiving element of the light-receiving element array, and resolution switching means for switching the resolution for each 1/N (N is a natural number), wherein the number of the plurality of light-receiving elements is a multiple of 2N.
According to still another aspect of the present invention, there is provided an image sensor comprising a plurality of photoelectric conversion devices each including a light-receiving element array in which a plurality of light-receiving elements are arranged, scanning means driven by a first shift register drive pulse for reading a signal from an odd-numbered light-receiving element of the light-receiving element array and a second shift register drive pulse for reading a signal from an even-numbered light-receiving element of the light-receiving element array, and resolution switching means for switching the resolution for each 1/N (N is a natural number), wherein the number of the plurality of light-receiving elements is a multiple of 2N.
According to still another aspect of the present invention, there is provided an image sensor having a plurality of photoelectric conversion devices each including a plurality of light-receiving elements, comprising resolution switching means for switching a resolution; control means, respectively, arranged in the photoelectric conversion devices, for changing signal read from the light-receiving element in accordance with the resolution switched by the resolution switching means; and signal read means for reading the signal from the light-receiving element in accordance with a plurality of pulses, wherein the signal read means periodically drives the plurality of pulses, and the number of light-receiving elements is set so that a signal read first from each of the signal read means in each photoelectric conversion device is read using the same pulse of the plurality of pulses.
According to still another aspect of the present invention, there is provided an image sensor having a plurality of photoelectric conversion devices each including a plurality of light-receiving elements, comprising resolution switching means for switching a plurality of resolutions changing every 1/N; control means for changing a signal read from the light-receiving element in accordance with a resolution switched by the resolution switching means; and signal read means for reading the signal from the light-receiving element in accordance with M (positive integer) shift register drive pulses, wherein the number of the plurality of light-receiving elements is a multiple of Mxc3x97N.
The above and other objects, features, and advantages of the present invention will be apparent from the detailed description of preferred embodiments in conjunction with the accompanying drawings.